Theft of articles of merchandise, especially from retail stores, is a continual problem. This problem can be dealt with in many ways, such as with technology. One technical solution is electronic article surveillance systems. A tag, label, or marker is secured to an article to be protected. The tag responds to an interrogation signal from a transmitting apparatus situated either at the exit door of the premises to be protected or at the aisle-way adjacent to the cashier or check-out station. A receiving coil on the opposite side of the exit or aisle-way from the transmitting apparatus receives a signal produced and emitted by the tag in response to the interrogation signal. The response signal may indicate that the tag has not been removed or deactivated and, hence, the article bearing it may not have been paid for or properly checked-out.
Several different types of tags are in use. In one type, the functional portion of the marker consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit. When placed in an electromagnetic field transmitted by an interrogation apparatus, the antenna-diode tag generates harmonics of the interrogation frequency in the receiving antenna. The detection of the harmonic or signal level change indicates the presence of the marker tag. A second type of marker consists of a first elongated element of high magnetic permeability ferromagnetic material disposed adjacent to at least a second element of ferromagnetic material having higher coercively than the first element. When subjected to the interrogation frequency of electromagnetic radiation, the tag causes harmonics of the interrogation frequency to be developed in the receiving coil.
Electronic article surveillance systems of the type discussed above have been shown to be effective in preventing the theft or unauthorized removal of articles, particularly articles which are small in size and relatively expensive. Two such small, but relatively expensive, articles which are vulnerable to theft are the compact disc (CD) and the digital video disc (DVD). CDs and DVDs are typically stocked and sold in generally flat, rectangularly shaped plastic containers or within a rectangular display container relative to software and video packaging. Thus, because of the size and shape of the containers it is relatively easy for a thief to remove one or more CDs or DVDs from the containers with little concern about being caught.